The present invention relates to an oscillator circuit utilizing the charging and discharging of a capacitor, and more particularly to such a circuit having means for switching between different oscillating frequencies.
The present invention is also concerned with an oscillator circuit which is particularly suitable for use as a tone ringer of a telephone set which alternately generates a high frequency tone such as 1400 Hz and a low frequency tone such as 400 Hz.
A conventional oscillator circuit of this kind is enabled to alter the output frequency either by switching between the outputs of a plurality of oscillator circuits or by varying the time constant of one oscillator circuit. Switching between oscillator circuits has the disadvantage of complexity resulting from the increased number of circuits, because of the need for a plurality of oscillator circuits. The varying of a time constant has an inability to make the plurality of oscillating frequencies widely different from one another on account of the difficulty involved in setting the plurality of frequencies independent of one another and of the difficulty involved in varying the time constant over a wide range.